This invention relates to a pneumatic jack, and more particularly to a pneumatic jack having a hydraulic locking control.
Hydraulic jacks, as well as pneumatic jacks, are well known in the art.
Moreover, pneumatic jacks incorporating means for retarding the descent of the jack when the air pressure upon the jack is removed, are shown in the U.S. Hemmeter Pat. Nos. 3,173,659 and 3,182,959. The Hemmeter Pat. No. 3,173,659 discloses a pneumatic jack having a hydraulic damper and also a mechanical locking mechanism for holding the jack in elevated positions, even in the absence of compressed air. The Hemmeter Pat. No. 3,182,959 discloses a pneumatic jack in which the descent of the jack is retarded, but not stopped, by a hydraulic mechanism.
The following U.S. patents disclose various types of hydraulic jacks in which the motive power for the hydraulic fluid is supplied by compressed air acting upon an intermediate piston head;
U.S. Pat. No. 552,274 Cole Dec. 31, 1895
U.S. Pat. No. 957,536 Baker May 10, 1910
U.S. Pat. No. 1,418,651 Johnson June 06, 1922
U.S. Pat. No. 1,903,887 Widener April 18, 1933
U.S. Pat. No. 2,638,075 Towler May 12, 1953
However, all of the above patents disclose jacks in which the lifting is accomplished through the movement of the hydraulic fluid being acted upon by the compressed air. Moreover, the rise of the jack head is limited to the length of the hydraulic cylinder.
The U.S. Notenboom et al Pat. No. 3,279,755 issued Oct. 18, 1966, discloses a multi-stage hydraulic hoist.
The U.S. Moor Pat. No. 3,743,248 issued July 3, 1973, discloses a multi-stage pneumatic jack in which the telescoping cylindrical shaft sections are surrounded by a rubber bellows. However, the bellows are described as being for protection of the jack from dust and the elements, and do not have any lifting function whatsoever.
A pneumatic jack 130 incorporating a flexible air bag is disclosed in the Granning U.S. Pat. No. 3,235,181, issued June 13, 1967. However, the Granning pneumatic jack is not provided with any means for holding the jack in extended position, or retarding its collapse by any means, if the air pressure fails.